The invention relates to a hydrodynamic coupling, in particular a hydraulic transmitter, specifically having the features from the preamble of claim 1.
A wide range of designs of hydrodynamic couplings with clutches for synchronization, in particular in the form of friction clutches actuated by centrifugal forces, are known. As a representative sample in this context, reference is made to the following documents:
1. DE 31 19 171
2. Shinko Engineering Co., LTD xe2x80x9cShinko Fluid Couplingsxe2x80x9d, EFK.012 1 100782T
3. xe2x80x9cHydromechanical Couplingsxe2x80x9d
4. DE 17 75 184
Each of these embodiments comprises a hydrodynamic coupling, in particular a hydraulic transmitter, which operates on the basis of the Fxc3x6ttinger principle and in which, by means of a pump impeller, mechanical energy in the form of rotational energy of the drive shaft, is converted into kinetic energy, i.e. flow energy of the operating medium, this flow energy, on the output side, being converted back into rotational energy by a further bucket wheel. The operating medium used is primarily oil, and in some special cases also water.
Hydrodynamic couplings of this type substantially comprise at least three parts, two bucket wheels, one outer wheel and one inner wheel which is enclosed by a coupling shell which is coupled to the outer wheel. The function of the bucket wheels as pump impeller and turbine wheel is generally dependent on the direction of power transmission, taking the direction of rotation into account. If the pump impeller is driven, i.e. the outer wheel or the inner wheel, a circuit of the operating medium is formed in the radial and axial planes in the toroidal working space between outer wheel and inner wheel. In the process, a circumferential force, which transmits the torque, and additionally an axial force are active. The circuit is maintained for as long as there is a difference in torque in the form of what is known as the slip S between the drive side and the output side. If both bucket wheels are running synchronously, the circuit breaks up and no further torque is transmitted. In this case, a hydrodynamic coupling, in nominal operation, is generally designed for 2 to 3 percent slip, i.e. the efficiency is then approximately 97 to 98 percent. To improve the efficiency, it is necessary to connect a friction clutch in parallel. In order, however, to maintain the start-up properties of the hydrodynamic coupling which are particularly advantageous on account of the hydrodynamic power transmission, in particular the property of gentle acceleration of extremely large masses with virtually zero wear, this friction clutch may only be shifted with a low slip. The design of the parallel circuit of the friction clutch and its arrangement or association with respect to the hydrodynamic coupling is known, in various designs, from the above-mentioned documents. In the design described in document DE 31 19 171, the friction clutch comprises two clutch halves, which can be actuated by a fluid pressure which is dependent on centrifugal force. In this case, a shift element which actuates the clutch, preferably a piston which can be displaced in the axial direction and a pressure chamber, which can be filled with liquid and in which, during rotation, a fluid pressure which is dependent on centrifugal force and acts to close the clutch, is built up, rotates with one half of the clutch. For this purpose, a reservoir which is separate from the shift element is provided in said clutch half, this reservoir being connected to the pressure chamber via at least one fluid line. A control element controls the degree of filling of the pressure chamber with liquid as a function of the rotational speed of the said clutch half. In this case, with the reservoir arranged closer to the axis of rotation of the clutch than the pressure chamber, the end faces which delimit the pressure space are matched to one another in such a manner that the volume of the pressure chamber adopts a value of virtually zero when the clutch is open. When a clutch of this type is coupled to a hydrodynamic coupling, the secondary shaft, that is to say the shaft which is connected to the turbine wheel, is connected to one half of the friction clutch. When the clutch is closed, the pump impeller and turbine wheel of the hydrodynamic coupling rotate synchronously. In this embodiment, the synchronizer clutch is arranged outside the hydrodynamic coupling and has to be coupled to the latter in a corresponding way, which means that the structural size taken up is considerably increased in the axial direction and, in addition, the structural outlay is considerably increased.
In the embodiments described in the documents listed under 2 to 4, the synchronizer clutch, which is designed as a friction clutch, is integrated in the hydrodynamic coupling or forms a structural unit therewith. In the document mentioned under 2, the outer wheel is assigned the function of the pump impeller and the inner wheel is assigned the function of the turbine wheel. The coupling shell, which encloses the turbine wheel is designed to be extended in the axial direction and is used as a drum, in which centrifugal weights rotate, which are driven by driver elements on the inner wheel. In addition to the increased need for space, a considerable drawback is the particular design of the inner wheel, which has to be equipped with driver elements for the centrifugal weights, and this has to be taken into account even during production of the inner wheel, in design and in selecting the material used. The driver elements are in this case, according to the proposed solution, screwed to the inner wheel, which also considerably increases outlay on assembly. Furthermore, it is impossible to rule out operating disruption, since during operation loosening of the screw connections can cause considerable damage.
In the coupling designs which are described in the documents listed under 3 and 4, the inner wheel is assigned the function of the pump impeller and the outer wheel is assigned the function of the turbine wheel. In this case too, the synchronizer clutch is integrated in an elongated region of one of the elements, in particular of the inner wheel, by this elongated region being designed as a drum in which centrifugal weights rotate, but these weights are driven by driver elements on the outer wheel, in particular the turbine wheel. This solution also takes up considerable amounts of space in the axial direction in its installed position. The extended region has to be taken into account when producing the pump impeller, either requiring a single-part design when producing the casting or having to be connected to the pump impeller via an additional material-to-material bond. In the other case, corresponding connecting elements are to be provided, with the result that an increased outlay on assembly is to be noted in addition to the outlay on manufacturing technology.
The hydrodynamic couplings with synchronizer clutchesxe2x80x94either associated or integratedxe2x80x94which are known in the prior art all have the drawback that the structural length in the axial direction is increased considerably compared to a conventional hydrodynamic coupling without synchronization. Further drawbacks are the increased structural outlay, manufacturing outlay and installation outlay, with considerably increased costs as a result. Furthermore, on account of the connections which have to be produced between the individual elements when integrating the synchronizer clutch in the hydrodynamic coupling, it is impossible to rule out the possibility of malfunctioning or disruption as arise in the event of the driver elements and therefore also the centrifugal bodies coming loose, which may lead to substantial, and in some cases even irreparable, damage to the individual elements.
The invention is therefore based on the object of further developing a hydrodynamic coupling of the type described in the introduction with a synchronizer clutch in such a manner that the above-mentioned drawbacks are avoided. In particular, the aim is to find a solution which is distinguished by a low structural outlay, small overall size, low manufacturing and assembly outlay and therefore low costs. However, in functional terms there are to be no restrictions compared to the hydrodynamic couplings which are known from the prior art.
The solution according to the invention is characterized by the features of claim 1. Advantageous configurations are described in the subclaims.
In a hydrodynamic coupling comprising at least two bucket wheelsxe2x80x94one outer wheel and one inner wheel which is enclosed by a coupling shell which can be coupled to the outer wheelxe2x80x94there is an integrated synchronizer clutch, the latter having at least a first clutch element and a second clutch element, which can be operatively connected to one another in a frictionally locking manner at least indirectly, the two elements being formed by elements of the hydrodynamic coupling, in particular the inner wheel and the coupling shell. For this purpose, the inner wheel has at least two segments, which form centrifugal bodies which, as a function of the centrifugal force, allow a frictional lock between the inner wheel or the individual segments of the inner wheel, also referred to as inner-wheel segments, and the coupling shell. The individual segments of the inner wheel are for this purpose guided in such a manner that they can be moved or displaced at least in the radial direction, but in the circumferential direction, in the direction of rotation, can be connected in a rotationally fixed manner to an element which can be connected to the drive side or the output side.
There are numerous possibilities in terms of the design of the inner wheel or of the individual segments. In the most simple case, the segments are provided by dividing the inner wheel into a plurality of segments, which can all be coupled to the drive or output in such a manner that they can be displaced in the radial direction but are rotationally fixed in the circumferential direction. The division of the inner wheel always takes place in the vaned region of the inner wheel in the circumferential direction, so that when the segments are arranged in rows against one another in the circumferential direction, the structural unit of the inner wheel is formed.
The solution according to the invention makes it possible in a simple manner to integrate a synchronizer clutch into a hydrodynamic coupling, the integration not requiring any additional space whatsoever compared to a conventional hydrodynamic coupling without a synchronizer clutch, so that if necessary it can be retrofitted in drive systems with a hydrodynamic coupling without, for example, increasing the overall length. In addition to the fact that the overall length is kept the same in the axial direction as that of a conventional design without synchronizer clutch, the number of components required also scarcely rises. The structural and manufacturing outlay is low. The costs of a coupling of this type are low. The synchronizer clutch takes over the function of a lock-up clutch, since the hydrodynamic power split produced by the mechanical pressure coupling is bypassed. The synchronizer clutch can therefore also be referred to as a lock-up clutch.
There are numerous possibilities with regard to the design of the segments on the inner wheel. Preference is given to division into a plurality of segments, in particular three segments, which when arranged next to one another in a row in the circumferential direction form the structural unit of the inner wheel and which are identical in terms of their geometric dimensions and shape. This embodiment offers the advantage of the simple design of the guide for the segments, for example in the form of a triangular profiled shaft or profiled hub. The individual segments are in this case preferably produced from a single-piece bucket wheel which is divided into the individual segments by means of mechanical cutting processes, for example. With regard to the cutting processes employed, it is possible to use various cutting processes, but it is preferable to employ cutting processes which require no further surface treatment and also cause only a low waste of material.
To achieve the radial displaceability of the individual inner-wheel segments and the guidance in the circumferential direction which takes place at least during torque transmission, corresponding means are preferably provided. These means for providing guidance in the circumferential direction and in the radial direction may likewise be designed in various ways. The only crucial factor is that torque transmission be possible between the individual segments of the inner wheel and the guide means and furthermore that mobility in the radial direction be ensured. In the most simple scenario, this is achieved by means of positively locking connections. For this purpose, in the most simple scenario the means have a guide element which is provided with a corresponding profile, preferably in the form of a shaft or hub. The functions of displaceability and of torque transmission are made possible by the design of the mutually facing surface regions on the profiled shaft or hub and the segments of the inner wheel. To ensure the torque transmission, it is preferable to use embodiments which are distinguished by a simple design of the driver elements on at least one of the mutually facing surface regions of the segments of the inner wheel or the profiled shaft or hub. It is conceivable to form projections and recesses on one of the two elements, namely the outer circumference of the guide element and/or inner circumference of the segments, which come into operative connection with substantially complementary recesses and projections on the respectively opposite element, namely the inner circumference of the inner wheel segment or guide element. In this case, it is conceivable for the individual segments of the inner wheel, in terms of mobility in the circumferential direction, either
a) to be securely fixed, i.e. without play, or
b) prior to transmission of a torque to allow a limited degree of mobility in the circumferential direction around the guide element, i.e. for there to be some degree of play.
This means that in the first case there is a rotationally fixed connection irrespective of the occurrence of a circumferential force, while in the second case a rotationally fixed connection between the segments of the inner wheel and the guide element is only produced under the influence of a circumferential force. The displaceability of the segments in the radial direction is limited by the coupling shell.
One possibility of producing a rotationally fixed connection in the circumferential direction without play consists in linking the segments to the hub via rotary joints. For this purpose, a rotary joint is associated to each segment, in the rear region in the direction of rotation. The action of centrifugal force during rotation effects mobility of the segment about the axis of rotation and therefore, with regard to a component which describes the movement, the radial direction in the pivoting movement.
Preferably, at least three centrifugal bodies are formed by the inner wheel of the hydrodynamic coupling, which bodies are of identical design in terms of their shape and geometric dimensions. These are in this case guided on a profiled shaft or profiled hub which is connected, for example, to the output side when used in a drive train. The guidance preferably takes place, without requiring the influence of a circumferential force, in a rotationally fixed manner in the circumferential direction and displaceably in the radial direction. The profiled shaft or hub in this case has a substantially triangular cross section with rounded corner regions. In the installed position, i.e. when the segments of the inner wheel are being guided on the guide element or the guide means, these corner regions in each case lie in a plane which corresponds to the abutment plane of two inner-wheel segments which are arranged adjacent to one another in the circumferential direction. The abutment plane is in this case characterized by the surface regions, which face one another in the circumferential direction, of the inner-wheel segments coming into contact with one another, or lies in the region of the space between the two surface regions, which face one another in the circumferential direction in the installed position, of the inner-wheel segments when they do not abut one another. Another possibility consists in the driver elements in each case engaging only in one segment. In an embodiment with three segments and a triangular profiled shaft or hub, in each case one corner region of the profiled shaft or hub would then engage in a corresponding recess in a segment.
The concrete design of the driver profile is not linked to a specific embodiment, but rather is made taking account of the number of segments, so that in any situation displaceability thereof in the radial direction and torque transmission are ensured.
According to a further aspect of the invention, the selection of the weight of the individual segments results in the synchronization point being controlled. This offers the advantage that, depending on use requirements, it is possible to drive directly through to an earlier or later time when a certain slip is present.
In a further development of the invention, to increase availability corresponding material pairings are to be selected for the individual clutch elements which can be brought into operative connection with one another in a frictionally locking manner, namely the first clutch element in the form of the inner wheel or the segments of the inner wheel and the second clutch element in the form of the coupling shell. In the process, it should be ensured that the frictional pairing is as far as possible free from wear for a certain operating period. The frictional lock between the inner wheel or the individual segments of the inner wheel and the coupling shell may take place directly or indirectly via an intervening friction element. In the case of direct frictional connection, under the action of centrifugal forces the surfaces of the inner wheel which are formed by the outer circumference of the inner segments are pressed onto the surface formed by the inner circumference of the coupling shell or the surface region which is necessarily formed for the frictional lock. In the other case, it is in each case possible for either the inner wheel, in particular the individual inner-wheel segments, in the region of their outer circumference, or the surface regions which enter an operative connection, in a frictionally locking manner, with the surfaces on the outer circumference of the inner wheel to be provided, on the inner circumference of the coupling shell, with a friction lining. In this case, it is also conceivable for both elements to be designed with a friction lining. The designs with a friction lining offer the advantage that a friction pairing with particularly advantageous properties can be achieved irrespective of the type of material used for the individual elements of the synchronizer clutch, first clutch element or second clutch element, which are formed by the coupling shell and the inner wheel, and at the same time, depending on the material selected, inexpensive production of the elements of the hydrodynamic coupling, inner wheel or coupling disc is achieved. Furthermore, it is also possible to utilize standardized bucket wheels or coupling shells which are already used in other, conventional hydrodynamic couplings and simply to provide these components with a friction lining for the purpose of achieving an expedient design of the friction pairing.
The materials used for the outer wheel and the coupling shell are preferably conventionally employed materials, for example nodular cast iron. By selecting the weight of the centrifugal bodies and therefore of the inner segments, which is likewise material-dependent, it is possible to have a controlled influence on achieving an optimum transmission performance in the start-up range. The aim is to achieve a performance characteristic xcex*103 in a range between 2.0 and 2.5 inclusive in nominal operation. However, this presupposes that in the coupling designed according to the invention the centrifugal bodies and therefore the inner-wheel segments have a low mass, for example by weight-optimized design or by selecting a relatively lightweight material, for example being made from aluminum, while the remaining elements may be produced from any desired material. To produce a particularly wear-free friction pairing, the inner wheel is then provided, in the region of its outer circumference, with a friction lining, preferably in the form of bronze, at least in the regions which form a frictionally locking connection with the coupling shell under the action of centrifugal forces. There are numerous possibilities with regard to the arrangement of the frictional lining on the inner wheel and/or on the inner circumference of the coupling shell. The friction lining may be joined to the corresponding elements, namely outer circumference of the inner wheel or outer circumference of the inner-wheel segments and inner circumference of the coupling shell, in a non-positively locking manner, a positively locking manner or by material-to-material bonding.
According to a further aspect of the invention, means for absorbing the axial force on the inner wheel which is produced when the hydrodynamic coupling is filled with an operating medium, for example oil or water, and the rotation of the pump impeller which takes place as a result of the outer wheel being coupled to a drive machine. These means are formed either by guide means, in particular the driver profile on the guide element, for example the profiled shaft or profiled hub, or by an additional, further guide on the inner circumference of the coupling shell. The means for absorbing the axial forces are to be designed to absorb an axial force which acts in both directions, since the axial force acts in an alternating manner.